(1) Field of the Invention
The present invention relates to an abrasive sheet and a process for producing the same. Particularly, the present invention relates to a flexible abrasive sheet having an excellent mechanical strength, heat and water vapor resistance, and satisfactory grinding and cutting properties, and a process for producing the same.
(2) Description of the Related Art
A conventional flexible abrasive sheet is an emery paper composed of a paper substrate and abrasive particles adhered to a surface of the paper substrate with an adhesive. This type of conventional flexible abrasive sheet is disadvantageous in that it has a poor mechanical strength and heat resistance, and unsatisfactory grinding properties, due to a poor mechanical strength of the paper substrate and an unsatisfactory bonding strength of the abrasive particles to the paper substrate. Accordingly, the conventional flexible abrasive sheet is usually not used for an industrial grinding tool or for the abrasion of articles having an extreme hardness or which are difficult to grind.
U.S. Pat. No. 3,385,684 discloses a grinding wheel surface portion comprising a matrix resin consisting of a phenol-formaldehyde resin or an essentially linear aromatic polyimide resin having a second order transition temperature of 250.degree. C. or more and a room temperature modulus of at least 300,000 p.s.i., and abrasive particles of synthetic diamonds having a grit size of 200 to 100 Tyler screen size.
Also, U.S. Pat. No. 3,650,715 discloses an abrasive article comprising a matrix resin consisting of poly-N,N'(4,4'-oxydiphenylene) pyromellitimide, diamond particles, and compacted dendritic copper.
The above-mentioned grinding wheel surface portion or abrasive article is produced by molding a mixture of the matrix resin powder, abrasive (diamond) particles and, if necessary, an additive, in a mold and by heating the molded mixture at an elevated temperature under pressure.
The above-mentioned powder-molding method is not satisfactory to obtain a thin flexible abrasive sheet having a high heat resistance.
Accordingly, it is strongly desired in industry to obtain a thin flexible abrasive sheet and a process for producing the same which are completely free from the above-mentioned disadvantages.